NAT (Network Address Translator)

    This device conducts inbound and outbound data flow accordingly between Internet and your company's netwok

    A. There is usually an Internet router before data within LAN reaches Internet. It is functioning as a gateway preventing information leaking out or penetrating in. However, the way to configure your Internet router varies from one brand to another; please refer to the manual looking for keyword such as virutal server.


    Typical wireless access point & router may look like these

    B. It is recommended to choose a NAT-Loopback capable Internet router. With a non-NAT Loopback Internet router, users within the same network segment in office cannot access server resource through the public IP address or domain name. To resolve this issue, there are a few alternatives below:

    1. Simply purchase a NAT-Loopback capable Internet router and worry nothing.

    2. Configure separate internal DNS servers internally and externally for name resolution. It requires certain amount of maitenance efforts.

    3. Place a line of '' in c:\windows\system32\drivers\etc\hosts file in every LAN computer. However, colleagues have to add this line while in office and exclude it while walking out since this name resolution works only within office LAN.

    4. Change mail server name within mail client software to mail server internal IP when stepping in office. Change mail server name within mail client software to mail server public IP or domain name when out of office.

    C. Your mail server must use an internal IP off DHCP scope to avoid IP conflict and ensure the mail server IP stays static so it will not change after a server reboot or an Internet router reboot. This can be done within Windows' TCP/IP property.

    D. About a dozen of mail-related TCP ports have to be kept opened between your mail server host and the outside world. On Internet routers, it is often referred as Virtual Server or Port Forwarding. Ports are listed as below:

    1. SMTP / SMTP STARTTLS -TCP 25 / used for sending mails and SMTP & SMTP STARTTLS share the same port.

    2. SMTP Submission - TCP 587 / used as an alternative sending port.

    3. SMTP SSL - TCP 465 / used for SMTP SSL encrypted mail sending.

    4. POP3 - TCP 110 / used for receiving mails in POP3 mode.

    5. POP3 SSL - TCP 995 / used for POP3 SSL  encrypted mail receiving.

    6. IMAP v4rev1 - TCP 143 / used for receiving mails in IMAP4 mode.

    7. IMAP v4rev1 SSL - TCP 993 / usd for IMAP4 SSL encrypted mail receiving.

    8. HTTP (WebMail) - TCP 80 / used for logging in mail server through web browser. (optional)

    9. HTTP SSL (WebMail) - TCP 443 / used for logging in mail server through web browser with SSL. (optional)

    a. CalDAV & CardDAV - TCP 8008 / used for CalDAV & CardDAV protocol in non-SSL mode.

    b. CalDAV - TCP 8443 / used for CalDAV protocol in SSL mode.

    c. CardDAV - TCP 8843 / used for CardDAV protocol in SSL mode.

    d. RDP - TCP 3389 / used for Remote Desktop Protocol to remotely control your mail server. (optional)

    E. EVO includes a feature of mail-related ports auto-checkup. It is located at Server setting status of Status Page and gives you an overview on whether ports are being properly opened on the Internet router.

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